Human herpes viruses are responsible for a variety of clinically significant diseases which, under certain circumstances, can be life threatening. Because viral DNA synthesis is central to the HSV replication process, identification and characterization of viral DNA synthetic enzymes and DNA structural elements required for initiation of DNA synthesis are essential prerequisites in efforts aimed at controlling HSV infection. Preliminary evidence has suggested the existence of a "viral DNA replication complex" composed of several virus-coded enzymes. The genetic studies proposed herein are designed to identify viral genes involved in HSV-1 DNA synthesis through the isolation and characterization of a series of isogenic temperature-sensitive (ts) mutants of HSV-1, 2) provide further genetic evidence for the existence of a viral DNA replication complex and identify its components through the isolation and mapping of ts+ extragenic suppressor mutations, and 3) localize and characterize the putative origin of replication located in the long unique region of the HSV-1 genome (ori(L)). It is anticipated that the availability of HSV-1 ts mutants in essential viral replication genes will not only serve to further our understanding of HSV DNA synthesis but will also identify viral enzymes as potential targets of antiviral chemotherapy.